It should be noted that if an invitation is arranged after the pilgrimages, because of being showy, proud or as a custom, then it is not right to host or attend it. However, if you feed the dear ones, relatives and friends as being grateful then it is lawful.
The Hadith says that when the Prophet (peace and blessings of Allaah be upon him) used to return from the journey, he would slaughter the animals and prepare a meal.
But doing so is neither Fardh nor Wajib, but is a Mustahab action.
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دلائل:
صحيح البخاری: (77/4)
عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ رَضِيَ اللَّهُ عَنْهُمَا: أَنَّ رَسُولَ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ لَمَّا قَدِمَ المَدِينَةَ، نَحَرَ جَزُورًا
أَوْ بَقَرَة۔
ALLAH Almighty knows best
DARULIFTA AL-IKHLAS,Karachi